The range of the electromagnetic spectrum in the near infrared within the range of wavelengths between 1 and 3 μm, plays a key role in the current socio-economic context. It is at the heart of communications on optical fibers and is frequently used in many applications related to detection of polluting gases and to safety. Consequently, attempts have been made for several years to find tuneable optical sources within this range of wavelengths, and with electrical pumping to guarantee compactness and ease of use. Semiconducting sources available at the present time (laser diodes, quantic cascade lasers) have very limited tunability based on control by temperature and/or injection current. For example, temperature tunability without mode skip of a DFB (Distributed Feedback Laser) is about 6 nm in the case of an InGaAsP diode within the telecom band (for a temperature excursion ΔT of about 50° C.), about 3 nm in the case of an InGaAsSb diode close to 2 μm (for a temperature excursion ΔT of about 13° C.), and about 20 nm for an InGaAs/AlAsSb cascade laser close to 3.35 μm (for a temperature excursion ΔT of about 90° C.).
An alternative approach to obtain a bright and tuneable coherent light source consists of making an electrically pumped Optical Parametric Oscillator (OPO). The basic principle of such a device is to use a semiconducting laser component emitting at a pump frequency ωp to parametrically generate radiation with two complementary frequencies, a signal frequency ωs and a complementary frequency ωc, satisfying the equation ωs+ωc=ωp, making use of the non-linear properties of the semiconducting material forming the laser.
If a cavity is defined for radiation at the signal frequency ωs and/or at the complementary frequency ωc, the component is genuinely an OPO. The OPO threshold above which the component emits two coherent light beams with signal frequency ωs and complementary frequency ωc is reached for a given pump power at pump frequency ωp. Throughout the remainder of this description we will call this component a “laser-OPO”. Its operating principle is shown in FIG. 1a. 
If no cavity is defined at the signal frequency ωs and/or at the complementary frequency ωc, or if the OPO threshold is not reached, the component emits pairs of photons by parametric fluorescence at signal frequency ωs and complementary frequency ωc simultaneously with very strong quantic correlations. It is well known that these pairs of so-called “twin” photons are very useful in the field of quantic communications, quantic information processing and metrology. In the following, we will refer to this component as “electrically pumped twin-photon source”. Its operating principle is shown in FIG. 1b. 
Other functions may be performed starting from a laser-OPO structure making use of parametric generation. For example, consider a laser-OPO above the laser threshold at the pump frequency ωp, but below the OPO threshold. If a coherent beam at the signal frequency ωs is optically injected into the component, optical parametric oscillation can be triggered and an amplified coherent beam at the signal frequency ωs, together with a coherent beam at the complementary frequency ωc, can be obtained. This component then acts as an amplifier at the signal frequency ωs, and as a frequency translator from the signal frequency ωs to the complementary frequency ωc. Its operating principle is shown in FIG. 1c. 
A major difficulty that has prevented the fabrication of an on-chip electrically pumped optical parametric oscillator in the past is namely obtaining the “phase-matching” condition between the different beams. If the parametric generation is to be efficient, the phase mismatch between the optical modes involved has to be cancelled. In the case of parametric fluorescence at degeneracy, in which a pump photon at the pump frequency ωp is split into two photons with the same energy, a signal photon at the signal frequency ωs and a complementary photon at the complementary frequency ωc according to the equation ωs=ωc=ωp/2, it corresponds to the condition n(ωp)=n(ωp/2), where n(ω) is the refraction index of a material at frequency ω.
In the general case, the frequency triplet should satisfy the following two conditions:Energy conservation: ωp=ωs+ωc Phase matching: ωp*n(ωp)=ωs*n(ωs)+ωc*n(ωc)
In a solid medium, phase matching is prevented by chromatic dispersion (refraction index increases as a function of the frequency). Phase matching can only be achieved in particular materials with optical birefringence, which makes it possible to achieve equality between indexes of two different polarisation modes. This birefringent phase matching is not possible in optically isotropic solid crystals such as gallium arsenide GaAs.
Confinement of pump, signal and complementary beams by wave guide provides new means of satisfying the phase-matching condition. Propagation of different guided modes is characterised by a specific effective index for each mode, and the effective index of a high order mode is lower than the index of the fundamental guided mode (at a given frequency ω). It then becomes possible to compensate for the effect of chromatic dispersion by this modal dispersion effect. By confining the beams, the waveguides provide better coverage of the three waves and a more efficient parametric generation.
In addition, III-V semiconducting waveguides widely used in optoelectronics have important additional benefits:                micro and nanoelectronic technologies enable very advanced engineering of optical heterostructures and high-level perfection of structures made;        the non-resonant quadratic non-linearity of these structures may have very high values due to the high value of the non-linear coefficient of GaAs in the near infrared (d14=100 μm/V);        III-V semiconducting materials have good thermal and mechanical properties and can resist very high optical intensities.        
In this context, A. Helmy discloses a method in document US2007/0104443 to obtain phase matching between different waves in a waveguide. According to this method, phase matching is obtained by combining the Total Internal Reflection (TIR) phenomenon with two Distributed Bragg Reflectors (DBR). Throughout the remainder of this document, the method disclosed in document US2007/0104443 is referred to as the “DBR-TIR” method.
Up to now, the DBR-TIR method has been the only method that has experimentally demonstrated parametric fluorescence by intra-cavity generation in a quantum well laser diode. FIG. 2 thus shows a parametric fluorescence laser diode 1 presented in the “Intracavity Parametric Fluorescence in Diode Lasers” document by B. J. Biljani et al. (CLEO 2011 conference proceedings, article PDPA3). The parametric fluorescence laser diode 1 comprises a semiconductor heterostructure 2 with a base 3 and a ribbon 4.
The base 3 of the semiconductor heterostructure 2 extends in a reference plane Oxy. The base 3 has a width Lb measured along the Ox axis. The base 3 comprises the following layers stacked along an Oz axis:                a semiconducting substrate 5 made of GaAs;        a first super-lattice 6 extending along the semiconducting substrate 5. The first super-lattice 6 is formed by a periodic stack of GaAs and GaAlAs sub-layers acting as a Bragg reflector at the pump wavelength of 1 μm;        a GaAlAs active layer 7 extending on the first super-lattice 6 and comprising multiple quantum wells, the multiple quantum wells emitting a pump wave at a pump wavelength of 1 μm;        a first part 8-1 of a second super-lattice 8, the first part 8-1 extending on the active layer 7, the second super-lattice 8 comprising a periodic stack of GaAs and GaAlAs sub-layers acting as a Bragg reflector at the pump wavelength of 1 μm.        
The ribbon 4 extends on the base 3 of the semiconductor heterostructure 2. The ribbon 4 has a width Lr that is measured along the Ox axis and is less than the width Lb of the base 3. The ribbon 4 comprises a second part 8-2 of the second super-lattice 8.
The first super-lattice 6 and the second super-lattice 8 provide vertical confinement of the pump wave by acting as Bragg reflectors at the pump wavelength. For signal and complementary wavelengths, the “Bragg reflector” effect is missing and vertical confinement of signal and complementary waves is achieved by total internal reflection. This is achieved by assuring that the first and second super-lattices 6 and 8 have a smaller average refraction index than the average refraction index of the active layer 7.
The parametric fluorescence laser diode 1 also comprises:                a first electrical contact 9 extending under the substrate 5 of the base 3;        a second electrical contact 10 extending on the ribbon 4.        
However, such a device has serious limitations:                it has a phase-matching condition that is extremely critical to obtain;        it only allows weak temperature tunability of the signal and complementary wavelengths;        it cannot achieve significant power levels, in other words of the order of a hundred nW, for signal and complementary wavelengths.        
In particular, this structure could not reach the OPO oscillation threshold. All these limitations severely restrict prospects of an on-chip electrically pumped optical parametric oscillator.
The two first difficulties mentioned above are related to the need to have easily adjustable free parameters to satisfy firstly the phase-matching condition and secondly to obtain frequency tunability of the component. For example, consider operation of the OPO at degeneracy (ωs=ωe=ωp/2). The solution obtained by solving the phase-matching equation, if there is a solution, is frequency ωpAP. It will be appreciated that the laser-OPO cannot function unless this frequency corresponds to the laser mode frequency. This is a genuine difficulty, because the phase-matching band is very narrow, typically of the order of 1 nanometer for GaAs/GaAlAs structures.
This point has important practical consequences because the laser-OPO fabrication process begins with epitaxial growth of the semiconductor heterostructure containing the active medium. After this first growth step, the spectral position of the gain curve for a given temperature is fixed, as is the position of its maximum that is close to laser mode. Therefore, there must be a control parameter that assures equality between the laser mode pump frequency ωp and the phase-matching frequency ωpAP.
The temperature T can be used as an adjustable parameter because it acts differently on the laser gain curve (and therefore on the pump frequency ωp) and on the phase-matching frequency ωpAP. In practice, such a parametric component is usually installed on a base with controlled temperature that allows fine control of the phase-matching condition. For example, this base makes it possible to compensate for the temperature rise of the laser component in operation, which can potentially result in losing the phase matching. Temperature may also be used to confer some spectral tunability to the component. Starting from one possible operating point at temperature T defined by triplet of frequencies (ωp(T), ωs(T), ωc(T)), where:                ωp(T) is the laser pump frequency at temperature T;        ωs(T) is the signal frequency at temperature T;        ωc(T) is the complementary frequency at temperature T;a change in the temperature T modifies the laser pump frequency and the effective indexes of the three modes. Consequently, phase matching will be obtained for different signal and complementary frequencies. Therefore, the temperature is a very useful parameter for fine control of the laser-OPO but it can only correct small deviations from the phase matching.        
On the other hand, optical guidance inside a ribbon made by deep etching provides a very efficient degree of freedom to vary the phase matching. “Ribbon made by deep etching” means a structure by which modes are confined laterally by etched flanks of the ribbon. In a laser diode, this means that the active medium is located in the ribbon. The phase-matching condition can be very well controlled by simple variation of the width of the deeply etched ribbon, if it is sufficiently narrow, typically of the order of a few micrometers wide. The ribbon width is also a parameter that can easily be adjusted during fabrication of the component, and that can be defined very precisely.
However, in the case of a quantum well laser diode, the recombination of electron-hole pairs on the lateral surfaces of the etched ribbon has a very prejudicial effect on functioning of the component. Due to this constraint, the width of a ribbon is always at least a few tens of micrometers wide in practice. Consequently, the parametric fluorescence laser diode shown in FIG. 2 uses a shallow etched ribbon 4: the active layer 7 is not in the ribbon 4 but is in the base 3. Shallow etching is sufficient to laterally localise modes, but it only has a very small effect on the effective indexes of the three modes and consequently on the phase-matching frequency at degeneracy ωpAP. More precisely, a variation of 3 to 5 μm in the ribbon width is not sufficient to shift ωpAP by more than 2 nm in the case of the structure studied by Biljani et al, while a shift of more than 20 nm could be obtained with the same structure if deep etching of the ribbon were possible.
This small margin in varying ωpAP is also the source of the second difficulty mentioned above: even if a phase-matching point is found, temperature tuning of the parametric process is impossible, and for example the signal frequency ωs and the complementary frequency ωe cannot be changed while maintaining their sum constant because the temperature modifies the pump frequency ωp. Using current injected into the laser as an adjustment variable is not a good idea either, for at least two reasons:
a) the variables I and T are related;                b) it is desirable that the power emitted by a photonic device can be modified independently of its wavelength.        
The third difficulty is related to the large series resistance of the experimental device used, as shown in FIG. 2. This large series resistance is itself due to band discontinuities in the bi-layers that form the distributed Bragg reflectors DBR, and to the thickness of these reflectors. One variant of this experimental device consists of replacing the upper distributed Bragg reflector by a total internal reflection confinement cladding. Such a modification provides a means of dividing the series resistance of the component by 2 but does not completely eliminate the problem. In the remainder of this document, this variant that combines a single distributed Bragg reflector with the total internal reflection phenomenon will be denoted by the abbreviation “SS-BRW”.